Wet electrostatic precipitators (WESP) have been used for many years to remove dust, acid mist and other particulates from water-saturated air and other gases by electrostatic means. In a WESP, particulates and/or mist laden water-saturated air flows in a region of the precipitator between discharge and collecting electrodes, where the particulates and/or mist is electrically charged by corona emitted from the high voltage discharge electrodes. As the water-saturated gas flows further within the WESP, the charged particulates matter and/or mist is electrostatically attracted to grounded collecting plates or electrodes where it is collected. The accumulated materials are continuously washed off by both an irrigating film of water and periodic flushing.
This type of system is used to remove pollutants from the gas streams exhausting from various industrial sources, such as incinerators, coke ovens, glass furnaces, non-ferrous metallurgical plants, coal-fired generation plants, forest product facilities, food drying plants and petrochemical plants.
The elimination of free moisture (mist) from the gas stream discharging from the WESP is often provided by mesh pads or chevrons located at the outlet from the WESP. Both have problems associated with them. Mesh pads are best suited for the removal of entrained droplets from particulate-free stream, with high removals being achieved at low micron sizes. However, pads often suffer plugging problems where fiber, particulates and/or VOCs (tars and sublimates) are present in the gas stream. Chevrons provide a high efficiency entrainment separation with limit drop sizes of 15 to 25 microns, depending on gas velocity and blade spacing, but can also suffer from plugging problems. These problems, in turn, lead to regions of excessive velocity causing droplet re-entrainment and carry-over.